Encapsulating materials having excellent light resistance and heat resistance are desired for high-power white LED devices whose application to generic illumination is being studied. In recent years, the so-called “addition curing type silicones” are frequently used.
The addition curing type silicones are obtained by thermally curing, in the presence of a platinum catalyst, a mixture including as main components a silicone derivative having a vinyl group in the main chain thereof and a silicone derivative having an SiH group in the main chain thereof. For example, patent document 1 discloses a resin composition into which an organopolysiloxane has been incorporated to regulate the molar ratio of silicon-bonded hydrogen atoms to alkenyl groups in the composition to a value within a specific range and from which a cured product having excellent transparency and insulating properties is therefore obtained.
Patent document 2 discloses a resin composition containing a silicone resin having at least two silicon-bonded alkenyl groups per molecule and an organohydrogensilane and/or organohydrogenpolysiloxane which has at least two silicon-bonded hydrogen atoms per molecule.
Patent document 3 discloses a composition that includes a combination of specific amounts of silicone resin ingredients having an SiH group, the silicone resin ingredients being a polyorganohydrogensiloxane which is linear and has a silicon-bonded hydrogen atom (Si—H group) somewhere in the molecular chain and a polyorganohydrogensiloxane which is linear and has an Si—H group at each of both ends of the molecular chain, and that hence gives a cured product having excellent strength.
On the other hand, for the addition curing type silicone resins, a highly active platinum catalyst is usually used. Because of this, once the curing reaction initiates, it is extremely difficult to stop the reaction in the course thereof. It is hence difficult to obtain a semi-cured state (stage B). It is known that addition of a phosphorus, nitrogen, or sulfur compound or an acetylene compound as a reaction inhibitor is effective in reducing the catalytic activity of the platinum catalyst (see, for example, patent document 4).    Patent Document 1: JP-A-2000-198930    Patent Document 2: JP-A-2004-186168    Patent Document 3: JP-A-2008-150437    Patent Document 4: JP-A-6-118254